Open-Response Homework Problem 7.3 Waking early on a cold, wintery morning, you

Question

Open-Response Homework Problem 7.3 Waking early on a cold, wintery morning, you decide to to go out

and start your car before going to class. When you step on your driveway, its icy surface is more slippery than

you expected, and you begin to slide down a 5 slope. At the bottom of your perfectly smooth driveway (5.0m

from your point of departure) there is a mailbox.

(a)[4 pts] What is your acceleration as you slide down the hill?

(b)[5 pts] For how long a time do you slide before you hit the mailbox?

(c)[5 pts] How fast are you going the instant before you hit the mailbox?

(d)[4 pts] Assume that the hill levels out right at the mailbox, so you make a smooth transition to moving

horizontally at the speed you just calculated. If your inertia is 70 kg, what is your momentum the instant

before you hit the mailbox?

(e)[6 pts] If you manage to avoid the mailbox, and instead grab a 6.5-kg cat, what is your new velocity the

instant after you grab the cat instead of hitting the mailbox?

Explanation / Answer

(a) Accelration a=gsin5=9.8*0.0871=0.854m/s^2

(b)Using s=0.5at^2

t^2=5*2/.854

t^2=11.707

t=3.42s

(c)Using v=u+at, u=0

v=.854*3.42

=2.92m/s

(d)Momentum p=mv where m=70kg

So, p=70*2.92

=204.54 Kgm/s

(e)By conserving momentum

204.54=(70+6.5)V'

V'=204.54/76.5

=2.67m/s

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